1. Technical Field of the Invention
The present invention relates to a swash plate type compressor for use in air conditioning system for vehicles and, in particular, to an improved structure of the swash plate therefor.
2. Description of the Related Art
A typical swash type compressor is disclosed, for example, in U.S. Pat. No. 4,431,378 to M. HATTORI et al, issued on Feb. 14, 1984, in which, as illustrated in FIG. 5, a pair of horizontal axially aligned cylinder blocks 1 forming a combined cylinder block are rotatably supported by a drive shaft 2 which also fixedly carries an iron swash plate 3. Inside the combined cylinder block are formed axially extending cylinder bores 4 arranged equi-angularly in the cross-section of the cylinder block. The cylinder block is closed at both ends by front and back housings 17, 19 via valve plates 16, 18. A double acting piston 5 made of aluminum is slidably fitted in the respective cylinder bore, and between the respective piston 5 and the swash plate 3, is arranged an iron shoe 6 in a semi-spherical shape with a predetermined shoe clearance both between the piston 5 and the shoe 6, and between the shoe 6 and the swash plate 3.
In the case of the above conventional iron swash plate, the slidability between the shoe 6 (made of iron) and the swash plate 3 is good because of the homogeneity of the material used. This iron swash plate, however, has an inherent drawback of a heavier weight. In addition, in the lower temperature atmosphere, the piston 5 (made of aluminum) contracts more than the iron swash plate 3 and the shoe clearance becomes smaller, resulting in a seizure therebetween. Conversely, the shoe clearance becomes larger when the compressor is operated at a high speed, and this causes abnormal noise.
Recently, it has been suggested to adopt an improved swash plate formed by aluminum material having a lower density so as to reduce a total weight of the compressor or minimize a moment of inertia of the moving mass, as disclosed in Japanese Unexamined Utility Model Publication (Kokai) No. 54-55711.
Some problems, however, have arisen in this attempt due to a far higher coefficient of thermal expansion of aluminum material relative to iron when the compressor fitted with the aluminum swash plate is operated in the low temperature atmosphere or when the respective parts thereof become hot during the high speed operation. That is, in the case of the aluminum swash plate, although the problems inherent to the iron swash plate are eliminated, other drawbacks arise of a reduced rigidity due to the softening property of the aluminum material in the high temperature and a lower slidability between the shoe and the swash plate during a high speed operation.